Liver cancer, especially hepatocellular carcinoma (HCC), affects the Hispanic population of the United States at a rate double that of the white population. This statistics has been evident since the early 70's, and continues to hold throughout the diverse American Hispanic population. The majority of people with HCC will die within 1 year of its detection. This high case-fatality rate can in part be attributed to lack of diagnostic methods that allow early detection. Cancer sera contain antibodies which react with a unique group of autologous cellular antigens called tumor-associated antigens (TAAs). Cancer has long been recognized as a multi-step process which involves not only genetic changes conferring growth advantage but also factors which disrupt regulation of growth and differentiation. It is possible that some of these factors could be identified and their functions evaluated with the aid of autoantibodies arising during tumorigenesis. The multi-factorial and multi-step nature in the molecular pathogenesis of human cancers must be taken into account in both the design and interpretation of studies to identify markers which will be useful for early detection of cancer. This application is focused on three specific aims: (1) to identify and characterize TAAs as markers in HCC using both approaches of SEREX (Serological Analysis of Recombinant cDNA Expression Libraries) and proteomic analysis; (2) to investigate the frequency of expression of identified TAAs in HCC using immunohistochemistry, and explore the relationship between antibodies in cancer sera and expression of corresponding targeted antigens in cancer tissue specimens to further validate the potential possibility of TAAs as markers in HCC; (3) to determine whether a mini-array of multiple TAAs would enhance antibody detection and be a useful non-invasive approach for immunodiagnosis of HCC. The rationale is that in sera from HCC patients who show autoantibody changes during progression from chronic liver diseases to HCC, novel autoantibodies appearing during this progression will likely be reporters of events associated with tumorigenesis, and therefore autoantibodies can be used as probes in SEREX and proteome-based approaches to identify antigens which are potentially involved in malignant transformation. Short abstract: The majority of people with hepatocellular carcinoma (HCC) will die within 1 year of its detection. This high case-fatality rate can in part be attributed to lack of diagnostic methods that allow early detection. In this study, we will determine whether a mini-array of multiple tumor-associated antigens would enhance antibody detection and further develop a useful non-invasive approach for the early detection of human HCC